Ziegler-Natta (ZN) type polyolefin catalysts are well known in the field of polymers, generally, they comprise (a) at least a catalyst component formed from a transition metal compound of Group 4 to 6 of the Periodic Table (IUPAC, Nomenclature of Inorganic Chemistry, 1989), a metal compound of Group 1 to 3 of the Periodic Table (IUPAC), and, optionally, a compound of group 13 of the Periodic Table (IUPAC) and/or an internal donor compound. ZN catalyst may also comprise (b) further catalyst component(s), such as a cocatalyst and/or an external donor.
Various methods for preparing ZN catalysts are known in the state of art. In one known method, a supported ZN catalyst system is prepared by impregnating the catalyst components on a particulate support material. In WO-A-01 55 230, the catalyst component(s) are supported on a porous, inorganic or organic particulate carrier material, such as silica.
In a further well known method the carrier material is based on one of the catalyst components, e.g. on a magnesium compound, such as MgCl2. This type of carrier material can also be formed in various ways. EP-A-713 886 of Japan Olefins describes the formation of MgCl2 adduct with an alcohol which is then emulsified and finally the resultant mixture is quenched to cause the solidification of the droplets.
Alternatively, EP-A-856 013 of BP discloses the formation of a solid Mg-based carrier, wherein the Mg-component containing phase is dispersed to a continuous phase and the dispersed Mg-phase is solidified by adding the two-phase mixture to a liquid hydrocarbon.
The formed solid carrier particles are normally treated with a transition metal compound and optionally with other compounds for forming the active catalyst.
Accordingly, in case of external carriers, some examples of which are disclosed above, the morphology of the carrier is one of the defining factors for the morphology of the final catalyst.
One disadvantage encountered with the supported catalyst systems is that distribution of the catalytically active compounds on the support material is dependent on the surface chemistry and the surface structure of the support material. As a result this may often lead to non-uniform distribution of the active component(s) within the catalyst particle. As a consequence of the uneven distribution of the active sites in catalyst particles catalysts with intra-particle in-homogeneities, as well inter-particle in-homogeneities between separate particles are obtained, which leads finally to in-homogeneous polymer material.
Further, support material will remain in the final polymer as a residue, which might be harmful in some polymer applications.
WO-A-00 08073 and WO-A-00 08074 describe further methods for producing a solid ZN-catalyst, wherein a solution of a Mg-based compound and one or more further catalyst compounds are formed and the reaction product thereof is precipitated out of the solution by heating the system. Furthermore, EP-A-926 165 discloses another precipitating method, wherein a mixture of MgCl2 and Mg-alkoxide is precipitated together with a Ti-compound to give a ZN catalyst.
EP-A-83 074 and EP-A-83 073 of Montedison disclose methods for producing a ZN catalyst or a precursor thereof, wherein an emulsion or dispersion of Mg and/or Ti compound is formed in an inert liquid medium or inert gas phase and said system is reacted with an Al-alkyl compound to precipitate a solid catalyst. According to examples said emulsion is then added to a larger volume of Al-compound in hexane and prepolymerised to cause the precipitation.
In general, a drawback of such precipitation methods is the difficulty to control the precipitation step and thus the morphology and average particle size of the precipitating catalyst particles.
Furthermore, the precipitation of the catalyst component(s) results easily in formation of broad particle size distribution of catalyst particles comprising particles from very small particles to big agglomerates, and further to the loss of the morphology of the catalyst and formation of fines. In polymerisation process this causes in turn undesired and harmful disturbances, like plugging, formation of polymer layer on the walls of the reactor and in lines and in further equipments, like extruders, as well decreased flowability of polymer powder and other polymer handling problems.
WO 03/000757 describes a process for the preparation of an olefin polymerisation catalyst component, enabling to prepare solid particles of a catalyst component comprising a group 2 metal together with a transition metal, however without using any external carrier material or without using conventional precipitation methods, but using so called emulsification-solidification method for producing solid catalyst particles
WO 2004/029112 discloses a further modified process of the method described in said WO 03/000757 for preparing an olefin polymerisation catalyst component having increased activity at higher temperatures.
U.S. Pat. No. 5,413,979 describes a further method for the preparation of a solid procatalyst composition wherein support materials are impregnated with catalyst component precursors in order to obtain a catalyst component.
U.S. Pat. No. 4,294,948 finally discloses a process for preparing an olefin polymer or copolymer, employing a solid titanium catalyst component prepared by treating pulverized catalyst precursors with organo metallic compounds of a metal of any of groups I or III of the Periodic Table, characterized in that the catalyst preparation occurs using pulverized, solid and particulate precursor materials.
EP 1403292 A1, EP 0949280 Al, U.S. Pat. No. 4,294,948, U.S. Pat. No. 5,413,979 and U.S. Pat. No. 5,409,875 as well as EP 1273595 A1 describe processes for the preparation of olefin polymerisation catalyst components or olefin polymerisation catalysts as well as processes for preparing olefin polymers or copolymers.
The above-outlined prior art procedures, in particular the processes for preparing olefin polymerisation catalyst components as outlined in WO 03/000757 typically comprise bis(2-ethyl-hexyl phthalate) (often called dioctylphthalate, DOP) as internal donor. The process for preparing such catalyst components usually involves the preparation of the donor in situ by reacting a precursor of this internal donor, typically phthaloyldichloride (PDC), with an alcohol, typically 2-ethyl-hexanol, in order to provide the internal donor outlined above. Alcohol is thus an essential part of the donor and its preparation. Consequently, the type of the donor is always dependent on the used alcohol. Further, said WO 03/000757 teaches the formation of the liquid-liquid two-phase system by using of a specific type of alcohol, namely said 2-ethyl-hexanol. In this process described in said WO 03/000757 formation of said two phase system, is very sensitive towards changes in conditions and chemicals and their concentrations. This sensitivity has restricted the use of other types of alcohols and thus other types of donors, or even prevented preparation of the catalyst component without any donor at all in catalysts prepared according to the basic teachings of said WO 03/000757, i.e. preparation of the catalyst without using any external carrier but using emulsification-solidification technique. Because the formation of the two-phase system requires use of alcohol and the donor precursor, it has not been possible to add donor as such during the preparation of catalysts as described here.
Accordingly, it would be highly advantageous if processes for preparing olefin polymerisation catalyst components would be available which allow the formation of catalyst components via the liquid-liquid two-phase system as for example outlined in WO 03/000757, in which processes stable liquid-liquid two phase system could be formed without the strong dependency of the alcohol and donor (donor precursor). This kind of preparation method would broaden the preparation window of the catalyst, and thus would give more possibilities to use desired donors without affecting the formed liquid-liquid two-phase system, which is essential to get the desired excellent morphology of the catalyst.
Thus the main object of the invention is to provide a method for preparing a catalyst having excellent morphology and which method allows to use different type of donors or even not to use any donor at all.
An additional object of the invention is provide a catalyst obtainable by a process as herein described.
Further one object of the invention is to use the catalyst as herein described in olefin polymerisation process.
Possibility of using desired donors in catalyst would make it possible to change the type of catalyst, and thus result in giving the practitioner greater latitude towards the use of most suitable catalyst for desired polymerisation processes and polymers.
Accordingly, it is the object of the present invention to overcome at least one of the problems identified above and to provide a process for preparing an olefin polymerisation catalyst via the liquid-liquid two-phase system. In embodiments, it is an object of the present invention to provide such a process for producing catalyst components making it possible to use different types of donors or even without the use of any internal donor. In further preferred embodiments, it is the object of the present invention to provide such a process allowing a greater latitude towards process conditions.